The invention relates to sensing of the identity at least one of multiple cables or wires arriving at a backplane connector of an apparatus designed for (accepting cards/modules for) combining and splitting high frequencies and low frequencies signals to and from a subscriber line, commonly referred to as a twisted pair, and more particularly to responsively providing an indication near the backplane connector that a remote probe has been connected to a common ground at a main distribution frame (MDF).
Current voice telephone operators are generally engaging in a growth phase of deploying data services to their subscribers. One of the chief ways to do this is to offer digital subscriber lines (DSL) wherein both voice and data may be carried over a common twisted pair cable to a subscriber""s residence or business. The twisted pair then carries two types of duplexed signals over different frequency bands. The first signal is the voice signal, generally at 4 KHz and below. The second signal is the data signal, generally modulated at above 4 KHz.
To add the connection of data, which is generally between an internet service provider (ISP) and the subscriber, a splitting apparatus or low pass filter (LPF) splits the data signals from the voice signals, and routes the data signals through a data link to the ISP. Such a data link may be wired or fiber optic. The additional equipment is sometimes referred to as a Digital Subscriber Line Access Multiplexer (DSLAM). In essence, adding a DSLAM means that the DSLAM must be inserted into the twisted pair circuit between a central office (CO) of the telephone equipment operator, and the premises wiring of the subscriber. The most common place to do that is at a patch panel which may be near a switching office of the operator. Note that the DSLAM does not provide switching of voice signals. The DSLAM combines signals incoming to the subscriber line: high frequency data signals on one hand, and low frequency voice signals on the other hand.
The installation of the DSLAM typically entails breaking the link from twisted pair subscriber line to the switch, and adding two additional connections: 1) from twisted pair subscriber line to the DSLAM, and 2) from DSLAM to the switch. In total, there must be an additional four wires added to the patch panel per addition of data services to a subscriber. The selection of these wires must be done carefully, because the wires from the DSLAM determine the routing of the data to specific ports of the DSLAM. Secondly, the polarity of these wires must observe the tip and ring conventional voltages established by the voice switching industry.
The DSLAM installation is complete when the DSLAM provides output signals corresponding to the now-distinct data channel of the subscriber twisted pair.
A DSLAM rack may have several shelves or racks devoted to the first set of connections, i.e. the four wires that attach to the patch panel for each subscriber installation. At least one shelf is referred to as the low pass filter shelf (LPFS) for the reason that the circuits on the shelf generally filter low frequency signals to be admitted from the subscriber twisted pair to the switch using a low pass filter (LPF) as is known in the art. High frequency signals are passed to other parts of the DSLAM for further processing as data signals.
Each shelf of LPFs may have multiple cable bundles that attach at a backplane that go to the patch panel. In addition, the DSLAM may have at least one shelf devoted to the multiplexing of data signals for ingress into the data network, e.g. the internet. This shelf may have wiring of ports of a line card to a specific LPF of the LPFS. Thus each LPF slot may have a confluence of signals that are purely data (LCS), purely voice (switch) and a combined voice over data signal (subscriber twisted pair).
Identifying the correspondence of bundled wire pairs to a port may be done using conventional means, wherein a technician consults a wiring chart to identify two of 50 bundled wires that correspond to one of a 6 by 8 matrix of ports of the LCS. The wiring chart often refers to the wires by a color coding on the outer insulator of the wires. Such a look-up process may require a technician to hold a reference manual in what is often a crowded central office or other telephony infrastructure enclosure. This is done at a time the technician also separates the needed wires by hand. This has to be done first with one wiring bundle dedicated to the subscriber twisted pair interface, and then next with a second wiring bundle dedicated to the central office twisted pair interface. Sometimes colors, and stripes on the outer insulator can be mistaken for other colors, particularly where 50 wires are concerned. An added difficulty develops because there is a moderate incidence of color blindness in the technician population. This problem is equally applicable where the bundle attaches to the patch panel in a common connector, e.g. 50 conductors in the connector.
A further risk occurs because there is a possibility for a defect to develop in one of several connectors necessary to route signals. For example, from patch panel subscriber twisted pair to patch panel central office twisted pair, there may be as many as 8 connectorized cables. In addition, there may be two cards that are installed to the DSLAM that connect to the backplanes, which make an additional 2 more connections that could be faulty.
Thus it would be helpful to verify the 10 or so interfaces that are added between subscriber line conductor and the interface to the plain old telephone service (POTS) network by performing a continuity check for such circuits. In addition, a means to identify the polarity of tip and ring associated with a LCS port would also be helpful.
An embodiment may be a circuit board sized to fit inside a vacant slot of a telephony filter, such as a DSLAM. The circuit board may be a height above a bottom edge of the circuit board so that a reciprocal connector engages a backplane communication connector that may provide electrical continuity to a main distribution frame (MDF). The circuit board may provide a positive voltage node above a common ground, wherein the positive voltage node may power an indicator having a probe input. The probe input may be connected to the reciprocal connector so that when a wire having a remote end at the MDF is connected to a common ground, the indicator illuminates.
Another embodiment may be a pair of circuit boards. One is a Line Card (LC) circuit board, which has a connector with a plurality of pins capable of mating to a slot-to-slot interface. The LC circuit board has an indicator having a positive voltage node applied to an indicator such as an LED and a probe input that is connected to a pin of the slot-to-slot interface. A LPF circuit board may mate to part of the slot-to-slot interface via a connector having a plurality of pins. The LPF circuit board may carry a single pole, double throw switch, wherein the single pole is electrically coupled to the probe input. The switch may move the single pole to a first throw to connect a subscriber conductor of the MDF. The switch may be moved to the second throw position to be connected to the central office (CO) conductor of the MDF.
Yet another embodiment may be an indicator having a positive voltage node and a probe input, wherein the probe input is connectable to the conductor of the line card connector (backplane). Any coupling of the probe input to ground causes the indicator to light up.
The use of one or more of the embodiments of the invention may enable a determination of completed cabling and accurately identify an identity of a wire or probe at a remote end to a DSLAM or other filtering apparatus. Such a wire or probe may be positively identified as connecting to a particular slot and particular port of a rack of equipment.
One or more of the embodiments may permit a selection of which type of cable an indicator should sense connection to, i.e. cables directed to a subscriber""s twisted pair, and theoretically able to transport voice and data signals. Alternatively, selection may be made to sense connection of cables directed to a publicly switched public network (PSTN), which may theoretically be filtered to carry only voice signals.
One or more of the embodiments is arranged to be portable, and suited to mate with connectors that may be part of a slot-to-slot interface such that the embodiment may be easily installed and removed from a interface that is under test. Such a configuration may aid rapid testing of many similarly shaped slot and slot-to-slot interfaces that have substantially the same type of connectors. Such testing made in advance of installing Low Pass Filter (LPF) and Line Cards (LC) may improve the speed with which a circuit of a DSLAM is inserted into the path between the PSTN and the subscriber line. In addition, technicians making such installations may break the link between subscriber line and PSTN for a briefer time than absent use of an embodiment.